Scanning projector with multipath beam relay

ABSTRACT

A scanning projector for a display apparatus includes a first scanning reflector configured to steer a light beam in a first plane, a second scanning reflector configured to steer the light beam received from the first scanning reflector in a second plane, and beam relay optics configured to relay a first pupil defined at the first scanning reflector to a second pupil defined at the second scanning reflector, and to relay the second pupil to an output pupil of the scanning projector. The beam relay optics may include a concave reflector and a polarization beam splitter coupled to a scanning reflector in a triple pass configuration.

TECHNICAL FIELD

The present disclosure relates to optical scanners and in particular toscanning projectors for near-eye displays.

BACKGROUND

Head mounted displays (HMD), helmet mounted displays, near-eye displays(NED), and the like are being used increasingly for displaying virtualreality (VR) content, augmented reality (AR) content, mixed reality (MR)content, and they are finding applications in diverse fields includingentertainment, education, training and biomedical science, to name justa few examples. The VR/AR/MR content can be three-dimensional (3D) toenhance the experience and to match virtual objects to real objectsobserved by the user. Eye position and gaze direction, and/ororientation of the user may be tracked in real time, and the displayedimagery may be dynamically adjusted depending on the user's headorientation and gaze direction, to provide a better experience ofimmersion into a simulated or augmented environment.

Compact display devices are desired for head-mounted displays. Because adisplay of HMD or NED is usually worn on the head of a user, a large,bulky, unbalanced, and/or heavy display device would be cumbersome andmay be uncomfortable for the user to wear.

Scanning projector displays provide images in angular domain, which canbe observed by an eye directly, without an intermediate screen or adisplay panel. The lack of a screen or a display panel in a scanningprojector display enables size and weight reduction of the display.Compact and efficient scanners such as tiltable MEMS reflectors may beused to provide a miniature scanning projector suitable for use in a NEDand NED-like displays.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described in conjunction with thedrawings, in which like elements are indicated with like referencenumerals, which are not to scale, and in which:

FIG. 1 is a schematic block diagram of a two-stage image projectorhaving two beam steering reflectors coupled in series;

FIG. 2 is a schematic block diagram of an embodiment of the imageprojector of FIG. 1 with beam routing optics in each of the two scanningstages;

FIG. 3 is a schematic block diagram of a near-eye display (NED) usingthe image projector of FIG. 1;

FIG. 4A is a schematic side cross-sectional view of an exampleimplementation of a two-stage image projector with a tiltable reflectorand polarization-controlled beam relay at each scanning stage;

FIG. 4B is a schematic front view of the example image projector of FIG.4A;

FIG. 5A is a schematic diagram of the image projector of FIGS. 4A and 4Bgenerally illustrating beam focusing and collimation by its opticalelements;

FIG. 5B is a schematic diagram illustrating the operation of an outputlens of the projector of FIGS. 4A-5A;

FIG. 6 is a schematic plan view of a MEMS scanner;

FIG. 7 is a schematic diagram of an embodiment of the image projector ofFIGS. 4A-5A with an alternative placement of tiltable reflectors;

FIG. 8 is a schematic diagram illustrating elements of an NED using theimage projector of FIG. 4A;

FIG. 9 is a flowchart of a method for forming a 2D image using twoscanning reflectors;

FIG. 10 is a schematic diagram illustrating an NED device including atwo-stage scanning projector having a first stage for forming a 2D imagein a FOV defined in an angle space, and a second stage operable to shiftthe FOV in the angle space responsive to changes in a user's gazedirection;

FIG. 11 is an isometric view of an example head-mounted display usingthe scanning projector of the present disclosure;

FIG. 12 is a block diagram of a virtual reality system including theheadset of FIG. 11; and

FIG. 13 is a functional block diagram of an example autonomous wearabledisplay system according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art. All statements herein reciting principles,aspects, and embodiments of this disclosure, as well as specificexamples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents as well asequivalents developed in the future, i.e., any elements developed thatperform the same function, regardless of structure.

As used herein, the terms “first”, “second”, and so forth are notintended to imply sequential ordering, but rather are intended todistinguish one element from another, unless explicitly stated.Similarly, sequential ordering of method steps does not imply asequential order of their execution, unless explicitly stated.

The terms “pupil relay”, “pupil relay system”, “pupil relay optics”, andthe like relate to an optical system that defines one or more opticalpaths between a first pupil and a second pupil, and which transfers abeam incident at a first pupil to a second pupil located at somedistance away from the first pupil. In a pupil relay as understoodherein, light beams emanating from the first pupil at different anglessubstantially overlap at the second pupil. Thus, a pupil relay operatingwith scanned beams transfers a variable beam angle at the first pupil toa variable beam angle at the second pupil, substantially without lateralshifts in the beam position at the second pupil. Here substantiallymeans with some tolerance that may be related to various inaccuracies inthe optical system and components thereof, and may mean for examplewithin +\−10% of the diameter of the light beam at the second pupil, andpreferably within +/−5% of the diameter of the light beam at the secondpupil, depending on system design and tolerances. The tolerance tolateral displacement may depend on the energy profile of the beam. Forexample, a Gaussian beam profile truncated at the 1/e² beam diameter maybe more tolerant to pupil relay lateral shifts than a flat “top hat”distribution of the beam energy along the same diameter. The first andsecond pupils may be defined by optical components of the system inwhich the pupil relay is used, such as reflectors and lenses. The term“pupil relay magnification” refers to an increase in size of the beamfrom the first to the second pupil. A pupil relay may image the firstpupil onto the second pupil.

The term “field of view” (FOV), when used in relation to an opticalsystem, may define an angular range of beam propagation supported by thesystem. A FOV may be defined by angular ranges in two orthogonal planescoplanar with an optical axis or a portion thereof. For example, a FOVof a NED device may be defined by a vertical FOV, for example +\−20°relative to a horizontal plane, and a horizontal FOV, for example +\−30°relative to the vertical plane. With respect to a FOV of a NED, the“vertical” and “horizontal” planes or directions may be defined relativeto the head of a standing person wearing the NED. Otherwise the terms“vertical” and “horizontal” may be used in the present specificationwith reference to two orthogonal planes of an optical system or devicebeing described, without implying any particular relationship to theenvironment in which the optical system or device is used, or anyparticular orientation thereof to the environment. The terms “NED” and“HMD” may be used herein interchangeably.

An aspect of the present disclosure relates to a 2D scanning projectorcomprising: a first scanning stage comprising a first scanning reflectorconfigured to steer an input light beam in a first plane; a secondscanning stage comprising a second scanning reflector configured tosteer the input light beam received from the first scanning stage in asecond plane; and, beam relay optics configured to relay a first pupildefined at the first scanning reflector to a second pupil defined at thesecond scanning reflector, and to relay the second pupil to an outputpupil of the scanning projector.

An aspect of the present disclosure relates to a system and method forscanning a beam of light in two dimensions using two or moresequentially disposed 1D or 2D scanning reflectors.

An aspect of the present disclosure provides a scanning projector for adisplay apparatus, comprising: a first scanning reflector configured tosteer a light beam in at least a first plane; a second scanningreflector configured to steer the light beam received from the firstscanning reflector in at least a second plane; and, beam relay opticsconfigured to relay a first pupil defined at the first scanningreflector to a second pupil defined at the second scanning reflector,and to relay the second pupil to an output pupil of the scanningprojector. In some implementations the second scanning reflector isconfigured so that the second plane is generally orthogonal to the firstplane.

In some implementations the beam relay optics comprises a firstpolarization beam splitter (PBS) and a first concave reflector coupledto the first PBS, wherein the first PBS is disposed in a triple-passconfiguration for routing the light beam sequentially to the firstscanning reflector and to the first concave reflector in a first twopasses, and toward the second scanning reflector in a third pass.

In some implementations the scanning projector comprising a waveplatedisposed in an optical path of the light beam for converting apolarization state thereof to an orthogonal polarization state betweenconsecutive passes through the first PBS.

In some implementations a lens may be disposed in an optical path of thelight beam upstream of the first scanning reflector. In someimplementations the lens may comprise an output lens disposed at theoutput pupil.

In some implementations the first PBS may be disposed to direct thelight beam sequentially to the first scanning reflector in the firstpass and to the first concave reflector in the second pass. The beamrelay optics may further comprise a second PBS and a second concavereflector coupled to the second PBS. The second PBS may be disposed in atriple-pass configuration to direct the light beam received from thefirst PBS sequentially toward the second scanning reflector and towardthe second concave reflector in a first two passes through the secondPBS, and toward the output pupil in a third pass.

In some implementations the beam relay optics may further comprise fourquarter-wave plates (QWP), one QWP proximate to each of the firstscanning reflector, the second scanning reflector, the first concavereflector, and the second concave reflector, for converting apolarization of the light beam between consecutive passes through eachof the first and second PBS.

In some implementations the first PBS may be disposed to direct thelight beam reflected from the first scanning reflector toward the firstconcave reflector, and from the first concave reflector toward thesecond PBS. In some implementations a first focusing lens may bedisposed upstream from the first PBS, and an output focusing orcollimating lens may be disposed at the output pupil of the scanningprojector. In some implementations the first focusing lens may beconfigured to cooperate with the first concave reflector to converge thelight beam to a focus at an intermediate location in an optical pathbetween the first and second scanning reflectors. In someimplementations a second focusing lens may be disposed proximate to thesecond scanning reflector. In some implementations the first concavereflector and the second focusing lens cooperate to relay the firstpupil to the second pupil with a magnification. In some implementationsthe second scanning reflector may be greater in area than the firstscanning reflector.

In some implementations each of the first and second scanning reflectorscomprises a tiltable MEMS reflector.

An aspect of the present disclosure provides a method for forming animage, the method comprising: providing a light beam to a first scanningreflector; responsive to a first image signal, steering the light beamin a first plane with the first scanning reflector; relaying the lightbeam from the first scanning reflector onto a second scanning reflector;responsive to a first image signal, steering the light beam with thesecond scanning reflector in a second plane; and, relaying the lightbeam from the second scanning reflector to an output pupil at an angledefined by steering angles of the first and second scanning reflectorsand substantially without an angle-dependent lateral spatial shift. Therelaying the light beam from the first scanning reflector onto a secondscanning reflector or from the second scanning reflector to the outputpupil may comprise using a first concave reflector and a first PBS in atriple-pass configuration.

In some implementations the method may comprise using the first PBS andthe first concave reflector to direct the light beam from the firstscanning reflector to the second scanning reflector, and using a secondPBS coupled to a second concave reflector to direct the light beam fromthe first PBS sequentially toward the second scanning reflector and theoutput pupil.

In some implementations the method may comprise changing a polarizationstate of the light beam to an orthogonal polarization state betweenconsecutive passes through each of the first and second PBS.

An aspect of the present disclosure provides a near-eye display (NED)device comprising: a support structure for wearing on a user's head; alight source carried by the support structure for providing a lightbeam; a pupil expander carried by the support structure; and, a scanningprojector carried by the support structure. The scanning projector maycomprise a first scanning reflector configured to steer the light beamin at least a first plane, a second scanning reflector configured tosteer the light beam received from the first scanning reflector in atleast a second plane, and beam relay optics configured to relay a firstpupil defined at the first scanning reflector to a second pupil definedat the second scanning reflector, and to relay the second pupil to anoutput pupil of the scanning projector. The pupil expander may beconfigured to expand the output pupil of the scanning projector in sizefor directing the light beam toward an eye of the user.

In some implementations the beam relay optics comprises a concavereflector, and a polarization beam splitter (PBS) that is disposed in atriple-pass configuration and is coupled to the concave reflector.

In some implementations one of the first and second scanning reflectorsmay be operable to scan light in two dimensions to form atwo-dimensional (2D) image in a field of view (FOV) defined in an anglespace, and the other of the two scanning reflectors may be operable toshift the 2D image in the angle space in response to a control signal.

Referring to FIG. 1, a two-stage scanning projector 100, also referredto as projector 100, is configured to receive an input light beam 101,and scan it angularly in two dimensions (2D). The input light beam isscanned using two successive beam scanning stages, a first scanningstage 110 and a second scanning stage 120, to produce an output lightbeam 151. The output light beam 151 may be scanned across a particularFOV, generally in 2D. In some embodiments, for example when projector100 is used in a display device, the input light beam 101 may betemporally modulated in coordination with the scanning, so that theoutput light beam 151 at the output of projector 100 renders a 2D imagein an angle space, which may be converted to a spatial image by anobserver's eye or by a focusing lens for displaying on a screen.

In some embodiments each of the first and second scanning stages 110,120 may be configured to scan a light beam it receives angularly in aparticular plane, and may be referred as a 1D scanning stage. In exampleembodiments described hereinafter, the first scanning stage 110 includesa first scanning reflector (SR) 111 configured to steer an input lightbeam in a first plane, while the second scanning stage 120 includes asecond SR 112 configured to steer the input light beam received from thefirst scanning stage 110 in a second plane. Each of the SRs 111 and 112may include, for example, a tiltable mirror or more generally a tiltablereflector (TR). However, embodiments using light steering devices otherthan tiltable reflectors may also be envisioned, such as those based oncontrollable refraction and/or diffraction of incident light. In atleast some example embodiments described below the planes in which thefirst and second SRs 111, 112 steer the input light beam aresubstantially orthogonal, which simplifies scanning the output lightbeam 151 in a raster scanning pattern. Here “substantially” means withcertain accuracy, for example +\−1°, or +\−3°, depending on systemdesign and tolerances. It will be appreciated however that scanning theinput beam sequentially in two planes that are neither orthogonal norparallel can also be used to produce a 2D scanning pattern. Non-parallelplanes may mean for example planes that are oriented at an angle of atleast 30° relative to each other. Embodiments in which the SRs 111, 112steer their respective input beams in a same plane could also beenvisioned, for example to scan the output scanning light beam 151 in awider angular range that may be supported by either of the SRs 111 or112, or to provide coarse and fine scanning separately.

Projector 100 may further include beam relay optics 121, 122 that relaythe input beam from the first SR 111 to the second SR 112, and from thesecond SR 112 to an output pupil 155 of the scanning projector 100. Inthe embodiment illustrated in FIG. 1, this beam relay optics isrepresented by a first beam relay 121 and a second beam relay 122. Thefirst beam relay 121 and the second beam relay 122 may be considered asparts of the respective first and second scanning stages 110 and 120 asshown, but may also be coupled thereto, and/or may share with them oneor more optical components. The first beam relay 121 may includerefractive and/or reflective optics that relays the beam reflected fromthe first SR 111 to the second SR 112, while the second beam relay 122may include refractive and/or reflective optics that relays the beamreflected from the 2^(nd) SR 111 to output pupil. The first beam relay121 and the second beam relay 122 may share one or more opticalcomponents, such as a lens in front of the second SR 112 that isdouble-passed as described below with reference to one or more exampleembodiments. The optics of the first beam relay 121 and the second beamrelay 122 may function as a pupil relay, relaying a first pupil definedat the first SR 111 to a second pupil defined at the second SR 112, andto relay the second pupil to an output pupil 155 of the scanningprojector. The output pupil 155 may be defined, for example, by anoutput focusing or collimating lens, as described below.

With reference to FIG. 2, there is illustrated an embodiment ofprojector 100 in which the first beam relay 121 includes first imagingoptics 131 and first routing optics 141, while the second beam relay 122includes second imaging optics 132 and second routing optics 142.Elements that are indicated in FIG. 2 with the same reference as in FIG.1 perform in the embodiment of FIG. 2 the same function as in theembodiment of FIG. 1, and may not be described again. Imaging optics 131and 132 may include one or more refractive and/or reflective opticalelements having optical power. In some embodiments, imaging optics 131may be configured to image a reflective surface of SR 111, or anoperating portion thereof, onto a reflective surface of SR 112, or anoperating portion thereof, so that the beam scanned by SR 111 impingesupon generally a same area of the second SR 112 for a range of scanningangles of SR 111. In some embodiments, imaging optics 132 may beconfigured to image a reflective surface of SR 112, or an operatingportion thereof, onto the output pupil 155, so that beam 149 incidentupon the output pupil 155 impinges upon generally a same area thereoffor a range of the scanning angles provided by the first and second SRs111, 112. The routing optics 141 and 141 may include one or more opticalelements that may be without optical power but are configured to routbeams incident thereon in desired directions. The first routing optics141 may rout the input optical beam from the first SR 111 to the secondSR 112, such as through, or engaging, one or more optical elements ofthe first imaging optics 131. The second routing optics 142 may rout theinput optical beam from the second SR 112 to the output pupil 155, suchas through, or engaging, one or more optical elements of the secondimaging optics 132. In some embodiments the routing optics 141 and 142may fold the optical path of the input beam to decrease the projectorfootprint, and may provide polarization-assisted multi-pass routing.

Referring to FIG. 3, there is schematically illustrated a display device300 using an embodiment of projector 100 to generate image light.Elements that are indicated in FIG. 3 with the same reference numeralsas in FIG. 1 and FIG. 2 perform in the embodiment of FIG. 3 the samefunction as in the embodiments of FIGS. 1 and 2, and may not bedescribed here again. As illustrated, the display device 300 may be anNED which provides angularly scanned image light to an eye 350 of theuser. A support structure 310, such as a monocular or binocular frame,may be configured for wearing on the head of a user. The supportstructure 310 may carry a light source 320, projector 100, and a pupilexpander 330. In binocular implementation, the support structure 310 maycarry two instances or these devices, one for each eye 350 of the user.In other embodiments the display device 300 may be configured to projectthe angularly scanned image light onto a screen. In some embodiments thepupil expander 330 may be absent or may be replaced with an objective orsuitable projecting optics configured to form a spatial image on ascreen. When implemented as a NED, the display device 300 may beconfigured to form virtual images. The light source 320 carried by theframe 310 provides the input beam 101 to projector 100, also carried bythe frame 310. The pupil expander 330 expands the output pupil 155 ofprojector 100 in area for presenting to the user's eye 350. The lightsource 310 may be configured to modulate the input light in time andspectrum to transmit images, and may be coupled to an image generatingprocessor 340 that provides corresponding timing and color selectionsignals to the light source 320. In RGB displays the light source 320may include, for example, sources of red, green, and blue light, such asred, green, and blue laser diodes (LDs) or light emitting diodes (LEDs),which light may be separately modulated in accordance with signals fromprocessor 340, and optically multiplexed to produce the input light beam101. From the light source 320, the input light 101 may be delivered toprojector 100 using, for example, a suitable optical waveguide such asan optical fiber, or bulk optical components, or in free space.Projector 100 scans the modulated input light beam 101 to produce theoutput light 151 beam that is 2D-scanned in the angle space within some2D FOV, as defined by angle scanning ranges of the SRs 111 and 112 and,possibly, aperture limitations of the beam routing optics of theprojector 100. The pupil expander 330 may then be used to expand theoutput pupil 155 of the projector for the viewer. The pupil expander 330may be for example in the form of an optical waveguide with an input andoutput couplers, with the output couplers generally being greater inarea that the input coupler or couplers. In one embodiment, the pupilexpander 330 is an optical waveguide having one or more input grating asan input coupler and one or more output gratings as the output coupler,with the gratings configured to match the FOV of projector 100 to arange of angles of total internal reflection (TIR) provided by thewaveguide. Although FIG. 3 shows a single projector 100 coupled to asingle optical source 320 at its input and a single pupil expander atits output, it will be appreciated that in binocular NEDs a separateprojector 100 coupled to its own light source 320 and its own pupilexpander 330 may be used for each eye of the user.

The beam relay optics of a scanning projector according to someembodiments of the present disclosure may include, in addition to firstand second SRs, a curved reflector, such as a concave mirror, which maycooperate with other optical elements of the projector to provide pupilrelay, and at least one polarization beam splitter (PBS) to implementpolarization controlled multi-pass beam routing. In some embodiments thePBS may be disposed in a triple-pass configuration to sequentiallydirect the input light beam toward a selected SR and a concave reflectorin a first two passes, and to direct the beam reflected from the concavemirror or the SR toward either the second scanning stage or toward anoutput pupil in a third pass.

Referring now to FIGS. 4A and 4B, there is illustrated an examplescanning projector 400 that may be viewed as an embodiment of thetwo-stage scanning projector 100 generally described above. The scanningprojector 400, which may be referred hereinafter simply as projector400, implements, among other features, polarization-assisted multi-passbeam routing, providing two-stage pupil relay in a compact footprint.FIG. 4A illustrates a cross-section of projector 400 in a plane ofincidence of an input beam 401 upon an input pupil 405 of the projector,while FIG. 4B illustrates projector 400 in projection on a planeorthogonal to the plane of incidence. In the following description aCartesian coordinate system (x,y,z) 477 may be used, in which the inputlight beam 401 is incident upon the projector in the direction of they-axis, and the two scanning stages of the projector are alignedgenerally in the z-axis direction. In the following description theinput light beam 401, as it traverses projector 400, may be referred toas the input beam 401, or as beam 401, or simply as “the beam”.Similarly to the projector 100 as generally described above, the inputlight beam 401 is passed through the two scanning stages in sequence,emerging from an output pupil 455 of the projector in the form of anoutput beam 403. The first scanning stage includes a first SR 411, whilethe second scanning stage includes a second SR 412. The output beam 403,which may be scanned with SRs 411 and 412 in sequence to produce animage, may also be referred to as the image beam 403. In the illustratedembodiment the first SR 411 is operable to steer the beam in a firstplane, while the second SR 412 is operable to steer the beam in a secondplane that may differ from the first plane. In the illustrated examplethe first plane may be the plane of the figure, which is also the (z,y)plane of the Cartesian coordinate system 477, while the second plane isgenerally orthogonal to the first plane, and may be described as an(x,y) plane of the coordinate system 477. The first SR 411 may be atiltable reflector (TR), such as a tiltable mirror, controlled by afirst actuator 461 to tilt it about an axis 417 parallel to the x-axis.The second SR 412 may also be a TR controlled by a second actuator 462to tilt it about an axis 419 parallel to the z-axis. In otherembodiments the tilt axes of SRs 411, 412 may have other relativeorientations.

In the illustrated embodiment the routing optics of projector 400includes a PBS in each of its two scanning stages, a first PBS 410 witha polarization routing surface 415 in the first scanning stage, and asecond PBS 420 with a polarization routing surface 425 in the secondscanning stage. The PBS 410, 420 may be in the form of, or include, PBScubes or prisms, but may also be embodied using other types ofpolarizers, for example using wire grid polarizers as the polarizationrouting surfaces 415, 425. The input pupil 405 may be defined by anoptional input lens 451. Input lens 451 may be disposed at an input of afirst scanning stage of the projector, such as at an input face or sideof the first PBS 410. The beam relay of the projector may be formed withtwo curved reflectors, a first concave reflector 431 optically coupledto the first SR 411 via PBS 410, and a second concave reflector 432optically coupled to SR 412 via PBS 420. The concave reflectors 431, 432may be each in the form of a concave mirror configured to fully, or atleast partially, reflect incident light. At the first scanning stage,the first PBS 410 is disposed in a triple-pass configuration to directthe input light beam 401 toward the second scanning stage aftersequential reflections from the first SR 411 and the first concavereflector 431. At the second scanning stage, the second PBS 420 isdisposed to receive the beam from the first scanning stage. The secondPBS 420 is optically coupled to the second SR 412 and the second concavereflector 432 in a triple-pass configuration to direct the beam receivedfrom the first scanning stage, toward the output pupil 455 afterconsecutive reflections from the second SR 413 and the second concavereflector 432. In the context of the present disclosure, “direct thebeam” may include allowing the beam to propagate therethrough without achange of direction.

In order to provide the desired beam routing by the respective PBS 410or 420, one or more polarization converters, such as one or morewaveplates, may be provided to convert the beam to an orthogonalpolarization between consecutive passes through each of the PBS. In theillustrated embodiment, a quarter-wave plate (QWP) may be providedproximate to each of the reflectors 411, 412, 431 and 432, so as to bepassed by the beam both on the way to and from a respective reflector,thereby changing the polarization of the beam to an orthogonalpolarization at each consecutive entrance of the PBS 410 or PBS 420.More particularly, a first QWP 441 may be provided in the optical pathbetween PBS 410 and SR 411, a second QWP 442 may be provided in theoptical path between PBS 410 and concave reflector 431, a third QWP 443may be provided in the optical path between PBS 420 and SR 412, and afourth QWP 444 may be provided in the optical path between PBS 420 andconcave reflector 432. In some embodiments QWPs 442 and 444 may belaminated onto respective PBS faces. In some embodiments QWPs 442 and444 may be laminated on the respective concave mirrors.

The beam routing in projector 400 may be understood by considering thepropagation of the input beam 401, which is illustrated in the figure byits central ray shown with a dotted line. The input beam 401 enters thefirst stage of the projector through an input pupil 405 as polarizedlight of a first polarization state, which may be denoted as LP1. Apolarization state orthogonal to LP1 may be denoted as LP2. In someembodiments, the polarization state LP1 may correspond to a linearp-polarization, as defined relative to its incidence upon the firstpolarization routing surface 415, with the LP2 corresponding to thelinear s-polarization. In some embodiments, the input light beam 401 maybe provided in the desired LP1 polarization by a light source (not shownin FIGS. 4A, 4B). In some embodiments an optional polarizer 407 may beprovided at the input pupil 405 of projector 400 to output the inputbeam 401 that is LP1-polarized. The input pupil 405 may be defined at afirst, or input, face or side of PBS 420. The first PBS 410 may beconfigured to optically couple the input pupil 405 to SR 411 in LP1polarization, and optically couple SR 411 to the concave reflector 431in LP2 polarization. The second PBS 420 may be configured to opticallycouple SR 412 to the second concave reflector 432 in one of LP1 or LP2polarization, and to optically couple the second concave reflector 432to the output pupil 455 in the other of the LP1 or LP2 polarization. AnLP1 to LP2 polarization converter 445, such as a suitably orientedhalf-wave plate (HWP), may be optionally provided between an output faceor side 414 of PBS 410 and an input face or side 421 of PBS 420.

In the embodiment illustrated in FIGS. 4A and 4B, the input light beam401 is p-polarized at the input pupil 405, and is transmitted toward SR411 in a first pass through PBS 410. After passing through QWP 441,which is oriented to change the polarization of the beam to circular,the beam is reflected off the first SR 411, which is shown forillustration in a tilted state. SR 411 steers the beam away from aninput axis C1 by twice the first tilt angle θ₁ of SR 411 about anx-directed axis 417 (FIG. 4B) in accordance with the laws of reflection.The input beam 401 steered by SR 411 may be referred as the firststeered beam 401A. The reflection off SR 411 directs the beam generallyback toward the first PBS 410 for a second pass therethrough. Passingthrough QWP 441 for a second time changes the beam to s-polarization (orLP2).

The second pass through PBS 410 re-directs the beam, now ins-polarization, toward the first concave mirror 431 via the second QWP442. A reflection off the first concave mirror 431 directs the beamgenerally back toward PBS 410 via a second pass through QWP 442, whichchanges the beam back to the p-polarization (LP1), which PBS 410transmits through. Thus the third pass through the first PBS 410 directsthe beam toward an output side or face 414 of PBS 410. An input side 421of the second PBS 420 may be located proximate to the output side orface 414 of PBS 410 to receive the beam therefrom. A half-wave plate 445may be disposed between the output face or side 414 of PBS 410 and theinput face or side 421 of PBS 420 to convert the beam to an orthogonalpolarization.

In the illustrated embodiment, the beam reflected from the concavemirror 431 passes through PBS 410 as p-polarized light, is converted bythe HWP 445 to s-polarized light, and is directed toward SR 412 byreflection off the polarization routing surface 425 in a first passthrough PBS 420. After passing through the third QWP 443, which isoriented to change the polarization of the beam to circular, the beam isreflected off the second SR 412, which steers the beam in accordancewith its tilt angle θ₂ about a z-directed axis 419 (FIG. 4B). Afterbeing steered by the second SR 412, the first steered beam 401A may bereferred as the image beam 401B.

The reflection off SR 412 directs the beam generally back toward PBS 420through the third QWP 443, which changes the beam to p-polarization. Thesecond pass through PBS 420 directs the beam through the polarizationrouting surface 425 and the fourth QWP 444 toward the second concavemirror 432. A reflection off the second concave mirror 432 directs thebeam generally back toward PBS 420 passing again through QWP 444, whichchanges the beam to the s-polarization. The third pass through PBS 420re-directs the s-polarized image beam 401B toward an output lens 453 andthe output pupil 455 by reflection upon the polarization routing surface425.

Referring to FIG. 5A, the operation of pupil replication or pupilimaging optics of projector 400 in one embodiment thereof isillustrated. An input beam 501, as it propagates through projector 400,is schematically outlined with dotted lines, which in this figureindicate the beam “edges”. Note that input beams that are narrower thanillustrated could be used. The beam propagation is illustrated fornominal, i.e. not tilted, positions of SR 411 and 412 by way of example;in these SR positions, the beam may have a substantially normalincidence at each of the SRs 411 and 412, and may also have on-axisincidence on the concave reflectors 431 and 432. Here substantiallynormal means accounting for fabrication tolerance, generally within+\−2°, or in some embodiments within +\−5°. In the illustratedembodiment the pupil replication is focal, i.e. the input beam 501 isnot collimated at the input pupil 405 of the projector, but converges atsome location on a focal surface 533, which may be within theprojector's first stage or between the stages. Embodiments with avirtual focus surface 533 located behind the concave reflector 431 mayalso be envisioned. In the illustrated embodiment an input focusing lens451 may be provided at the input facet or side of PBS 410 to provide aconvergent beam that has a size S₁ at the light reflecting face of SR411 in its nominal, not-tilted state. The input pupil 405 may be definedby a light-accepting face of lens 451, or a central portion thereof. S₁may represent, for example, the beam diameter at SR 411. The lightreflecting face of SR 411 defines a first pupil 511, which size may besubstantially S₁/cos(θ_(1max)) to avoid clipping the beam when the SR istilted, or slightly large to account for tolerances, for example 10%larger. Here, θ_(1max) represents a maximum tilt angle of SR 411expected during projector operation. In some embodiments the reflectingface of SR 411 may be elliptical.

The pupil replicating optics of projector 400 operates so as to make thelocation illuminated by beam 501 at the output pupil 455 substantiallyindependent on the tilt angle θ₁ of the first SR 411 and the tilt angleθ₂ of the second SR 412 within their respective angular ranges ofoperation. It provides an image beam 503 emanating from the output pupil455 that is capable of scanning in the angle space within theprojector's FOV substantially without lateral spatial displacement ofthe beam at the output pupil 455. Here substantially means accountingfor system tolerances, generally with a lateral displacement less than5% of the diameter of image beam 503 and preferably less than 10% of thediameter of the image beam in some embodiments.

In the illustrated embodiment the pupil replicating optics of projector400 includes the input focusing lens 451, two concave mirrors 431 and432, a second focusing lens 452 that may be disposed at the second SR412, and an output lens 453 disposed at the output pupil 455. In someembodiments the output pupil 455 may be at a distance from lens 453. Thefirst concave mirror 431 and the second focusing lens 452, which may bereferred to as the first pupil replicating optics or the first pupilrelay, cooperate to replicate or relay the first pupil 511 defined at SR411 onto a second pupil 512 defined at SR 412, so that the input beam501 hits the light reflecting face of SR 412 for any tilt angle θ₁ of SR411 within an operating range thereof, e.g. from −θ_(1max) to +θ_(1max).By way of example, θ_(1max) can be in the range from 10 to 40 degrees.The input lens 451 may cooperate with the concave mirror 431 to definethe focal surface 533 where beam 501 converges after reflecting off theconcave mirror 431. Lens 452 may be configured to cooperate with theconcave mirror 431 to image the first pupil 511 onto the second pupil512 with a magnification X, in which case the second SR 412 may begreater in size than the first SR 411 by a factor of X (linear). Themagnification factor X depends on the optical distance between SRs 411and 412, the radius of curvature of concave mirror 431, and to someextent on the optical power of lens 452, and may be suitably adjusted byvarying one or more of these parameters. The magnification factor X maybe greater than 1 when the optical path between SR 411 and the concavemirror 431 is shorter than the optical path between the concave mirror431 and SR 412. In some embodiments the optical power of the concavemirror 431 may be selected to image SR 411 to SR 412 with themagnification factor X. In embodiments in which the beam is relayed fromthe first SR 411 to the second SR 412 with magnification, the second SR412 may be proportionally greater in size than the first SR 411. By wayof example, in a projector with the pupil magnification X between thefirst and second SRs 411 and 412, the light reflecting face of SR 412,which defines the second pupil 512, may have a size of substantiallyX·S₁/cos(θ_(2max)), or slightly large to account for tolerances, forexample 10% larger. Here, θ_(2max) represents a maximum tilt angle of SR412 expected during projector operation. By way of example, θ_(2max) canbe in the range from 10 to 40 degrees. By way of a non-limiting example,X may be equal to 1.4+−10%.

The second concave mirror 432 and the output lens 453 cooperate with thesecond focusing lens 452 to relay the second pupil 512 onto the outputpupil 455, and may be referred to as the second pupil relaying optics orthe second pupil relay. The second focusing lens 452, which may beshared with the first pupil relay, may cooperate with the second concavemirror 432 and the output lens 453 to image the second pupil 512 ontothe output pupil 455. In embodiments where lenses 452 and 453 are closeto respective pupil planes, SR 412 may be imaged onto the output pupil455 primarily by the optical power of the concave mirror 431. The secondpupil relaying optics may replicate or relay the second pupil 512 to theoutput pupil 455 either with or without magnification.

Advantageously, in embodiments where the SRs 411 and 412 areorthogonally oriented 1D scanners, the FOV of projector 400 may beadjusted independently in two orthogonal planes, which may correspondfor example to the vertical and horizontal dimensions when used in aNED. When image beam 401B is steered by one of the first and second SRs411, 412, the image beam 401B may scan across an input face of theoutput focusing lens 453, changing the location of its incidence uponthe lens. The output focusing lens 453 is configured to convert thischange of location to a change in angle of the output beam 503. This isschematically illustrated in FIG. 5B, which shows image beams 501B1 and502B2, outlined by dotted and dashed lines, respectively, that areincident upon the output focusing lens 453. The two image beams 501B1and 501B2 may correspond to two different tilt angles of, for example,SR 411, and may be spatially shifted relative to each other as theyenter the output lens 453. These two image beams are converted by lens453 into output scanning beams 503 a and 503 b which substantiallyoverlap at the output pupil 455 generally without a lateral shifttherebetween, and emerge from it at different angles.

Referring to FIG. 6, each of the SRs 411 and 412 may be for example inthe form of a uni-axial MEMS scanner 600, where “MEMS” stands for amicro electro-mechanical system. It includes a scanning reflector 610,e.g. a mirror, supported by a pair of torsional hinges 601 allowingtilting the scanning reflector 610 about an “X” axis. The torsionalhinges 601 extend from the scanning reflector 610 to a fixed base 622,for tilting the scanning reflector 610 about “X” axis. Note that the “X”axis of FIG. 6 may represent either the x-axis or the z-axis of theCartesian coordinate system 477 of FIGS. 4A and 4B. Actuators may bedisposed underneath the scanning reflector 610 for providing a force foractuating the tilt of the scanning reflector 610 about the “X” axis. Theactuators may be electrostatic, electro-magnetic, piezo-electric, etc.For electrostatic mirror actuation, a comb drive may be located on thetorsional hinge members. For example, in the embodiment shown in FIG. 6,an actuator 631 may be disposed under an edge of reflector 610 to tiltthe scanning reflector 610 about X-axis. In some embodiments a biaxialscanning reflector may be used, in which torsional hinges 601 extendfrom the scanning reflector 610 to a gimbal ring (not shown), which issupported by a second pair of torsional hinges (not shown) extendingfrom the gimbal ring to the fixed base 322, for tilting the gimbal ringand the scanning reflector 610 as a whole about “Y” axis.

A feedback circuit 641 may be provided for providing feedbackinformation about the angles of tilt of the scanning reflector 610. Thefeedback circuit 641 may for example measure electric capacitancebetween the electrostatic actuator 631 and the scanning reflector 610 todetermine the tilt angle θ. Separate electrodes may also be providedspecifically for the feedback circuit 641. The capacitance may bemeasured via voltage measurements, and/or via a radio-frequency (RF)reflection from portion(s) of the scanning reflector 610 and a phasedetector using, for example, a frequency mixer and low-pass filter. Insome embodiments, a small magnet may be placed on the scanning reflector610, and a nearby pickup coil e.g. fixed to the base 622 may be used topick oscillations of the scanning reflector 610. Furthermore in someembodiments, an optical signal may be reflected from the scanningreflector 610 and a photodetector may be used to detect the reflectedbeam. The photodetector may or may not have spatial resolution. Forspatial resolution detectors, a detector array or a quadrant detectormay be used. Sync pulses or signals may be generated at specific anglesof tilt of the scanning reflector 610, e.g. when crossing a zero tiltangle.

In some embodiments, the first and second SRs 411 and 412 may beimplemented using two 1D MEMS tiltable reflectors 610 supported by twodifferent bases 622. In some embodiments, the first and second SRs 411and 412 may be implemented using two MEMS tiltable reflectors 610supported by the same base 622. In some embodiments, raster scan signalsmay be provided to each actuator 631 of the two tiltable reflectors 610with non-parallel, e.g. orthogonal, tilt axes to implement a 2D rasterscan pattern of the image beam. In some embodiments one or more tiltablereflectors 610 may be operated in a resonant mode for speed and energyefficiency. In the resonant mode of operation, a tiltable reflector 610oscillates about its tilt axis at a near-resonance frequency, and thebeam is pulse-modulated in time in accordance with an image pattern. Ina pair of tiltable reflectors such as 1D MEMS scanners coupled via apupil relay and oscillating about non-parallel axes, the oscillationsare decoupled from one another, which simplifies the overall trajectoryprediction.

It is noted that the 1D MEMS scanner 600 is only an example of a scannerimplementation. Many other implementations are possible, includingrefractive and diffractive beam scanners. When implemented with MEMS,various comb structures may be used to provide an increasedelectrostatic attraction force between electrodes. Comb and/or honeycombstructures may be used to stiffen the tiltable reflector 610. Thetiltable reflector 610 may include a mirror surface, a multilayerdielectric reflector, etc. The tiltable reflector 610 may be located atthe center of the 1D MEMS scanner 600, or may be offset from the centerif required. Two or more of 1D MEMS scanners with parallel and/ornon-parallel, including orthogonal, tilt axes may be supported by thesame base 622.

Referring back to FIGS. 4A, 4B, and 5A, the PBS 410 and 420 may be inthe form of, or include, polarization splitting cubes or prisms with oneof their optical axes aligned along a common optical axis C2, which maybe parallel to the z-axis in FIGS. 4A, 4B, with an output face 414 ofPBS 410 proximate to an input face 421 of PBS 420 and parallel thereto.The polarization routing surfaces 415 and 425 may be oriented at 45degrees to the common optical axis C2 of the two PBS. The PBS cubes orprisms embodying PBS 410 and 420 may be of the same size or of differingsizes. FIGS. 4A and 4B illustrate an embodiment with opticalmagnification from SR 411 to SR 412, as described above; in suchembodiments, PBS 410 may be physically smaller than PBS 420 in at leastone dimension as it routs a smaller-diameter beam.

Furthermore, in the example embodiment described above, SR 411 of thefirst steering stage is aligned with the input pupil 405 of theprojector, and is coupled therewith in transmission for p-polarization,while being coupled to the first concave mirror 431 in reflection fors-polarization. The optical axis of the concave reflector 431, definedby a vortex and a center of curvature thereof, may be generallyperpendicular to the direction of the first pass of the input beam 401through PBS 410. However, in other embodiments the input pupil 451, thefirst SR 411, and the concave mirror 431 may be positioned differentlyrelative to the output face 414 of PBS 410. For example, in oneembodiment the locations of SR 411 and concave mirror 431 may beswitched, in which case the input light beam 401 may be s-polarized atthe input pupil 405. In another embodiment, the locations of the inputpupil 405 and the first concave reflector 431 may be switched, with theinput light beam 401 again in the s-polarization state as it enters PBS410 for the first pass. Similarly, the positioning of SR 412, outputpupil 455, and the second concave mirror 432 relative to PBS 420 in thesecond stage may be different from the example embodiment illustrated inFIGS. 4A, 4B, and 5.

Furthermore, in the example embodiment described above the respectivepolarization routing surfaces 415, 425 of PBS 410 and 420 transmitp-polarized light and reflect s-polarized light. However, embodimentsmay be envisioned in which the polarization routing surfaces 415, 425 ofPBS 410 and 420 are configured to operate with other orthogonal pairs ofpolarization states. Furthermore, in some embodiments the respectivepolarization routing surfaces 415, 425 of PBS 410 and 420 may not beparallel to each other.

Generally, the second SR 412 and the second concave mirror 432 may bepositioned at any of five remaining “free” faces of PBS 420, with thepolarization routing surface 425 of the second PBS 420 suitably orientedto couple SR 412 to the input face 421 for one polarization state and tocouple SR 412 to the second concave reflector 432 in the orthogonalpolarization state. In some embodiments, the polarization routingsurfaces 415, 425 of PBS 410 and 420 may incline in different planes.

FIG. 7 illustrates an example embodiment 400A of projector 400 where theconfiguration of the second stage generally repeats that of the firststage with a 90 degree counter-clockwise rotation. In this exampleconfiguration, SR 412 is disposed at a PBS face 423 of PBS 420 acrossfrom the input PBS face 421 and is thus coupled thereto in transmissionfor p-polarized light. In this configuration, a HWP between PBS 410 and420 is not needed. The second concave mirror 432 is disposed with itsoptical axis at 90 degrees from the common optical axis C2 of PBS 410and 420, and across from the output pupil 455, so as to receives-polarized image light steered by SR 412 after it is reflected by thepolarization routing surface 425. In the illustrated embodiment theinput pupil 405 and the output pupil 455 are on the same side of theprojector. In another embodiment PBS 420 may be rotated by 180 degreesabout the C2 axis, so that the polarization routing surfaces 415, 425are parallel and the input pupil 405 and the output pupil 455 are onopposite sides of the projector.

Referring to FIG. 8, the projector 400 may be used in an NED device 800,referred to as NED 800 in the following, to generate a scanning imagebeam 803 that may be relayed to an eye 850 of a user to form an imagefor the user. In the illustrated embodiment the output pupil 455 ofprojector 400 is coupled to in input coupler 855 of a waveguide 810,which also has one or more output couplers 820 which may be configuredto expand the scanning image beam in size to provide an expanded imagebeam 833. In this embodiment, the waveguide 810 operates as a pupilexpander or pupil replicator. The input coupler 855 may be in the formof, or include, one or two diffraction gratings or one or two couplingprisms. It may be sized to match the output pupil 455 of projector 400.The output coupler or couplers 820 may be for example in the form of oneor more diffraction gratings, which in some embodiments may beholographically defined. By way of example, in one embodiment the inputcoupler 855 may be in the form, or include, a diffraction grating, suchas a relief grating, with a grating vector g₁, and the output coupler820 may be in the form, or include, a first output diffraction gratingwith a grating vector g₂ and a second output diffraction grating with agrating vector g₃, so that g₁+g₂+g₃=0. In such embodiments, an outputangle of the expanded output image beam 833 is equal to an angle atwhich the scanning image beam 803 from projector 400 impinges the inputcoupler 855, so that the waveguide 810 relays the output FOV ofprojector 400 to the user's eye 850 one to one. NED 800 may include animage signal generating processor 860 that provides electrical imagessignals V1 and V2 to the first and second SRs 411 and 412, respectively.These signals may define the beam steering angles of an output beam 803of the projector in two orthogonal planes, which may correspond to thevertical and horizontal scanning directions of an output beam 803 of theNED. The electrical images signals V1 and V2 may be synchronized withcolor and intensity modulation of the input beam 401 so that the NEDoutput beam 803 draws a 2D image in the angle space to be converted in aspatial image in the eye 850 of the user. Advantageously, performing thevertical and horizontal scanning of the image beam using two 1D scannersenables independent adjustment of their characteristics, such as pixeldensity, scan frequency, raster size, etc, and produce a morepredictable raster scan pattern than that available from biaxialscanners operating at near-resonance.

Referring to FIG. 9, there is illustrated a method 900 for scanning alight beam according to an embodiment of the present disclosure. In theflowchart, each box represents a step or operation that may be performedby a scanning projector example embodiment of which have been describedabove, or one or more elements thereof, and may be referred to generallyas a step. The method may include providing an input light beam to afirst SR at step 910, steering the input light beam in at least a firstplane with the first SR at step 920, relaying the input light beam fromthe first SR onto a second SR at step 930, steering the input light beamwith the second SR in a second plane at step 940, and at step 950relaying the input light beam from the second scanning reflector upon anoutput pupil at an angle defined by tilt angles of the first and secondscanning reflectors. In some embodiments, step 930 may include using afirst PBS coupled to a first concave reflector. In some embodiments,step 950 may include using a second PBS coupled to a second concavereflector. Step or operation 920 may include providing a firstelectrical image signal to an actuator of the first SR, with the firstSR steering the beam in the first plane by a first angle defined by thefirst electrical image signal. Step or operation 940 may includeproviding a second electrical image signal to an actuator of the secondSR, with the first to steer the beam in a second plane by a second angledefined by the second electrical image signal. Step or operation 950 maybe performed so that a position of the image beam at the output pupil isgenerally independent on tilt angles of the first and second scanningreflectors within operating tilt angle ranges thereof. In someembodiments the first plane may be orthogonal to the second plane. Insome embodiments the first plane may correspond to a vertical plane of atwo-dimensional FOV supported by the projector, and the second plane maycorrespond to a horizontal plane of the 2D FOV supported by theprojector.

In some embodiments, at least one of the two SRs 411, 412 may beconfigured as a 2D scanning reflector to scan the light beam it receivesin two different, for example orthogonal, planes. A 2D SR may beimplemented for example with a 2D tiltable reflector, such as a 2D MEMSreflector that is configured to tilt about two orthogonal axes. In oneembodiment the first SR 411 may be implemented with a 2D TR that isoperable to form a 2D image within an FOV defined in the angle space,and the second SR 412 as a 1D TR or a 2D TR operable to shift the FOV inthe angle space, for example in response to a user-related orimage-related signal. In some embodiments, these functions of the SR 411and 412 may be switched.

Turning to FIG. 10, a NED 1000 includes a light source 1006, a scanningprojector 1030 coupled to an image light source 1006, and apupil-replicating waveguide assembly 1040 coupled to the scanningprojector 1030. NED 1000 may be an embodiment of NED 800 describedabove. The scanning projector 1030 may be embodied as described abovewith reference to the scanning projectors of FIGS. 1-5B, 7, and 8. Inthe embodiment shown in FIG. 10, the scanning projector 1030 includesfirst 1052 and second 1002 tiltable reflectors, e.g. MEMS reflectorstiltable about one or two axes. The tiltable reflectors 1052 and 1002may represent the SRs 411 and 412 of the scanning projector 400 describeabove. A controller 1090 is operably coupled to the light source 1006,the first 1052 and second 1002 tiltable reflectors, and to an optionaleye tracker 1088. The function of the eye tracker 1088 is to determineat least one of position or orientation of a user's eye 1086 in aneyebox 1084, from which a gaze direction of the user may be determinedin real time.

In operation, the controller 1090 operates the first 1052 and second1002 tiltable reflectors to cause a light beam 1004 at the exit pupil ofthe scanning projector 1030 to have a beam angle corresponding to apixel of an image to be displayed. The controller 1090 operates theimage light source 1006 in coordination with the tiltable reflectors1052, 1002 to form an image in angular domain for displaying to theuser. The pupil-replicating waveguide assembly 1040 ensures that theimage may be observed by the user's eye 1086 at any position of theuser's eye 1086 in the eyebox 1084. In some embodiments, the eye tracker1088 is operated to determine the gaze direction of the user.

In embodiments where each tiltable reflector 1002 and 1052 is a 2Dtiltable reflector, one of them, e.g. the first tiltable reflector 1052,may be operated to scan the light beam 1004 in two non-paralleldirections to form the image in the angular domain while the other, i.e.the second tiltable reflector 1002, may be operated to shift the entireimage, i.e. to shift a FOV of the near-eye display 1000, towards thegaze direction of the user. The image being rendered by the controller1090 may be updated accordingly, i.e. shifted in opposite direction bythe same amount, to make sure that the virtual image is steady as theFOV is shifted. The resulting effect of “floating” FOV is similar toviewing a dark scenery by using a flashlight, where the flashlight isautomatically turned in a direction of user's gaze, illuminatingdifferent parts of a surrounding scenery depending where the user islooking at the moment. As the rate of FOV shift is determined by the eyemobility which is generally slower than speed of scanning, the firsttiltable reflector 1052 may be made smaller and faster, while the secondtiltable reflector 1002 may be made larger and slower. In someembodiment the second tiltable reflector 1002 may be operable to shiftthe image in one dimension only, for example along a horizontal axis ofthe NED.

Embodiments of the present disclosure may include, or be implemented inconjunction with, an artificial reality system. An artificial realitysystem adjusts sensory information about outside world obtained throughthe senses such as visual information, audio, touch (somatosensation)information, acceleration, balance, etc., in some manner beforepresentation to a user. By way of non-limiting examples, artificialreality may include virtual reality (VR), augmented reality (AR), mixedreality (MR), hybrid reality, or some combination and/or derivativesthereof. Artificial reality content may include entirely generatedcontent or generated content combined with captured (e.g., real-world)content. The artificial reality content may include video, audio,somatic or haptic feedback, or some combination thereof. Any of thiscontent may be presented in a single channel or in multiple channels,such as in a stereo video that produces a three-dimensional effect tothe viewer. Furthermore, in some embodiments, artificial reality mayalso be associated with applications, products, accessories, services,or some combination thereof, that are used to, for example, createcontent in artificial reality and/or are otherwise used in (e.g.,perform activities in) artificial reality. The artificial reality systemthat provides the artificial reality content may be implemented onvarious platforms, including a wearable display such as an HMD connectedto a host computer system, a standalone HMD, a near-eye display having aform factor of eyeglasses, a mobile device or computing system, or anyother hardware platform capable of providing artificial reality contentto one or more viewers.

Referring to FIG. 11, an HMD 1100 is an example of an AR/VR wearabledisplay system which encloses the user's face, for a greater degree ofimmersion into the AR/VR environment. The function of the HMD 1100 is toaugment views of a physical, real-world environment withcomputer-generated imagery, and/or to generate the entirely virtual 3Dimagery. The HMD 1100 may include a front body 1102 and a band 1104. Thefront body 1102 is configured for placement in front of eyes of a userin a reliable and comfortable manner, and the band 1104 may be stretchedto secure the front body 1102 on the user's head. A display system 1180may be disposed in the front body 1102 for presenting AR/VR imagery tothe user. The display system 1180 may for example include two opticalwaveguides for relaying scanning image beams to the eyes of the userfrom scanning projectors 1114. Sides 1106 of the front body 1102 may beopaque or transparent.

In some embodiments, the front body 1102 includes locators 1108 and aninertial measurement unit (IMU) 1110 for tracking acceleration of theHMD 1100, and position sensors 1112 for tracking position of the HMD1100. The IMU 1110 is an electronic device that generates dataindicating a position of the HMD 1100 based on measurement signalsreceived from one or more of position sensors 1112, which generate oneor more measurement signals in response to motion of the HMD 1100.Examples of position sensors 1112 include: one or more accelerometers,one or more gyroscopes, one or more magnetometers, another suitable typeof sensor that detects motion, a type of sensor used for errorcorrection of the IMU 1110, or some combination thereof. The positionsensors 1112 may be located external to the IMU 1110, internal to theIMU 1110, or some combination thereof.

The locators 1108 are traced by an external imaging device of a virtualreality system, such that the virtual reality system can track thelocation and orientation of the entire HMD 1100. Information generatedby the IMU 1110 and the position sensors 1112 may be compared with theposition and orientation obtained by tracking the locators 1108, forimproved tracking accuracy of position and orientation of the HMD 1100.Accurate position and orientation is important for presentingappropriate virtual scenery to the user as the latter moves and turns in3D space.

The HMD 1100 may further include a depth camera assembly (DCA) 1111,which captures data describing depth information of a local areasurrounding some or all of the HMD 1100. To that end, the DCA 1111 mayinclude a laser radar (LIDAR), or a similar device. The depthinformation may be compared with the information from the IMU 1110, forbetter accuracy of determination of position and orientation of the HMD1100 in 3D space.

The HMD 1100 may further include an eye tracking system for determiningorientation and position of user's eyes in real time. The obtainedposition and orientation of the eyes also allows the HMD 1100 todetermine the gaze direction of the user and to adjust the imagegenerated by the display system 1180 accordingly. In one embodiment, thevergence, that is, the convergence angle of the user's eyes gaze, isdetermined. The determined gaze direction and vergence angle may also beused for real-time compensation of visual artifacts dependent on theangle of view and eye position. Furthermore, the determined vergence andgaze angles may be used for interaction with the user, highlightingobjects, bringing objects to the foreground, creating additional objectsor pointers, etc. An audio system may also be provided including e.g. aset of small speakers built into the front body 1102.

Referring to FIG. 12, an AR/VR system 1150 includes the HMD 1100 of FIG.11A, an external console 1190 storing various AR/VR applications, setupand calibration procedures, 3D videos, etc., and an input/output (I/O)interface 1115 for operating the console 1190 and/or interacting withthe AR/VR environment. The HMD 1100 may be “tethered” to the console1190 with a physical cable, or connected to the console 1190 via awireless communication link such as Bluetooth®, Wi-Fi, etc. There may bemultiple HMDs 1100, each having an associated I/O interface 1115, witheach HMD 1100 and I/O interface(s) 1115 communicating with the console1190. In alternative configurations, different and/or additionalcomponents may be included in the AR/VR system 1150. Additionally,functionality described in conjunction with one or more of thecomponents shown in FIGS. 11 and 12 may be distributed among thecomponents in a different manner than described in conjunction withFIGS. 11 and 12 in some embodiments. For example, some or all of thefunctionality of the console 1190 may be provided by the HMD 1100, andvice versa. The HMD 1100 may be provided with a processing modulecapable of achieving such functionality.

As described above with reference to FIG. 11, the HMD 1100 may includethe eye tracking system 1118 for tracking eye position and orientation,determining gaze angle and convergence angle, etc., the IMU 1110 fordetermining position and orientation of the HMD 1100 in 3D space, theDCA 1111 for capturing the outside environment, the position sensor 1112for independently determining the position of the HMD 1100, and thedisplay system 1180 for displaying AR/VR content to the user. In someembodiments the display system 1180 includes (FIG. 11) a scanningprojector 1125. The display system 1180 may further include an opticsblock 1130, whose function may be to convey the images generated by thescanning projector 1125 to the user's eye. The optics block may includevarious lenses, e.g. a refractive lens, a Fresnel lens, a diffractivelens, an active or passive Pancharatnam-Berry phase (PBP) lens, a liquidlens, a liquid crystal lens, etc., a pupil-replicating waveguide,grating structures, coatings, etc. The display system 1180 may furtherinclude a varifocal module 1135, which may be a part of the optics block1130.

The I/O interface 1115 is a device that allows a user to send actionrequests and receive responses from the console 1190. An action requestis a request to perform a particular action. For example, an actionrequest may be an instruction to start or end capture of image or videodata or an instruction to perform a particular action within anapplication. The I/O interface 1115 may include one or more inputdevices, such as a keyboard, a mouse, a game controller, or any othersuitable device for receiving action requests and communicating theaction requests to the console 1190. An action request received by theI/O interface 1115 is communicated to the console 1190, which performsan action corresponding to the action request. In some embodiments, theI/O interface 1115 includes an IMU that captures calibration dataindicating an estimated position of the I/O interface 1115 relative toan initial position of the I/O interface 1115. In some embodiments, theI/O interface 1115 may provide haptic feedback to the user in accordancewith instructions received from the console 1190. For example, hapticfeedback can be provided when an action request is received, or theconsole 1190 communicates instructions to the I/O interface 1115 causingthe I/O interface 1115 to generate haptic feedback when the console 1190performs an action.

The console 1190 may provide content to the HMD 1100 for processing inaccordance with information received from one or more of: the IMU 1110,the DCA 1111, and the I/O interface 1115. In the example shown in FIG.12, the console 1190 includes an application store 1155, a trackingmodule 1160, and a processing module 1165. Some embodiments of theconsole 1190 may have different modules or components than thosedescribed in conjunction with FIG. 12. Similarly, the functions furtherdescribed below may be distributed among components of the console 1190in a different manner than described in conjunction with FIGS. 11 and12.

The application store 1155 may store one or more applications forexecution by the console 1190. An application is a group of instructionsthat, when executed by a processor, generates content for presentationto the user. Content generated by an application may be in response toinputs received from the user via movement of the HMD 1100 or the I/Ointerface 1115. Examples of applications include: gaming applications,presentation and conferencing applications, video playback applications,or other suitable applications.

The tracking module 1160 may calibrate the AR/VR system 1150 using oneor more calibration parameters and may adjust one or more calibrationparameters to reduce error in determination of the position of the HMD1100 or the I/O interface 1115. Calibration performed by the trackingmodule 1160 also accounts for information received from the IMU 1110 inthe HMD 1100 and/or an IMU included in the I/O interface 1115, if any.Additionally, if tracking of the HMD 1100 is lost, the tracking module1160 may re-calibrate some or all of the AR/VR system 1150.

The tracking module 1160 may track movements of the HMD 1100 or of theI/O interface 1115, the IMU 1110, or some combination thereof. Forexample, the tracking module 1160 may determine a position of areference point of the HMD 1100 in a mapping of a local area based oninformation from the HMD 1100. The tracking module 1160 may alsodetermine positions of the reference point of the HMD 1100 or areference point of the I/O interface 1115 using data indicating aposition of the HMD 1100 from the IMU 1110 or using data indicating aposition of the I/O interface 1115 from an IMU included in the I/Ointerface 1115, respectively. Furthermore, in some embodiments, thetracking module 1160 may use portions of data indicating a position orthe HMD 1100 from the IMU 1110 as well as representations of the localarea from the DCA 1111 to predict a future location of the HMD 1100. Thetracking module 1160 provides the estimated or predicted future positionof the HMD 1100 or the I/O interface 1115 to the processing module 1165.

The processing module 1165 may generate a 3D mapping of the areasurrounding some or all of the HMD 1100 (“local area”) based oninformation received from the HMD 1100. In some embodiments, theprocessing module 1165 determines depth information for the 3D mappingof the local area based on information received from the DCA 1111 thatis relevant for techniques used in computing depth. In variousembodiments, the processing module 1165 may use the depth information toupdate a model of the local area and generate content based in part onthe updated model.

The processing module 1165 executes applications within the AR/VR system1150 and receives position information, acceleration information,velocity information, predicted future positions, or some combinationthereof, of the HMD 1100 from the tracking module 1160. Based on thereceived information, the processing module 1165 determines content toprovide to the HMD 1100 for presentation to the user. For example, ifthe received information indicates that the user has looked to the left,the processing module 1165 generates content for the HMD 1100 thatmirrors the user's movement in a virtual environment or in anenvironment augmenting the local area with additional content.Additionally, the processing module 1165 performs an action within anapplication executing on the console 1190 in response to an actionrequest received from the I/O interface 1115 and provides feedback tothe user that the action was performed. The provided feedback may bevisual or audible feedback via the HMD 1100 or haptic feedback via theI/O interface 1115.

In some embodiments, based on the eye tracking information (e.g.,orientation of the user's eyes) received from the eye tracking system,the processing module 1165 determines resolution of the content providedto the HMD 1100 for presentation to the user using the scanningprojector 1125. In some embodiments, the processing module 1165 canfurther use the eye tracking information to adjust the image presentedwith the scanning projector 1125 to prevent vergence-accommodationconflict and/or to offset optical distortions and aberrations.

Referring to FIG. 13, a simplified block diagram of an exampleelectronic system 1200 is an example of a wearable display system forimplementing some of the embodiments disclosed herein. The electronicsystem 1200 may include one or more processors 1210 and a memory 1220.Processor(s) 1210 may be configured to execute instructions forperforming operations and methods disclosed herein and can be, forexample, a general-purpose processor or a microprocessor suitable forimplementation within a portable electronic device. Processor(s) 1210may be communicatively coupled to a plurality of components within theelectronic system 1200. To implement this communicative coupling, theprocessor(s) 1210 may communicate with other illustrated componentsacross a bus 1240. The bus 1240 may be any subsystem adapted to transferdata within electronic system 1200. The bus 1240 may include a pluralityof computer buses and additional circuitry to transfer data.

The memory 1220 may be operably coupled to the processor(s) 1210. Insome embodiments, the memory 1220 may be configured for short-termand/or long-term storage, and may be divided into several units. Thememory 1220 may be volatile, such as static random access memory (SRAM)and/or dynamic random access memory (DRAM) and/or non-volatile, such asread-only memory (ROM), flash memory, and the like. Furthermore, thememory 1220 may include removable storage devices, such as securedigital (SD) cards. The memory 1220 may provide storage ofcomputer-readable instructions, data structures, program modules, andother data for the electronic system 1200. In some embodiments, thememory 1220 may be distributed in different hardware modules. A set ofinstructions and/or code might be stored on the memory 1220. Theinstructions might take the form of executable code that may beexecutable by the electronic system 1200, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on the electronic system 1200 (e.g., using any of a varietyof generally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, the memory 1220 may store a plurality ofapplication modules 1222 to 1224, which may include any number ofapplications. Examples of applications may include gaming applications,presentation or conferencing applications, video playback applications,or other suitable applications. The applications may include a depthsensing function and/or an eye tracking function. The applicationmodules 1222 to 1224 may include particular instructions to be executedby processor(s) 1210. In some embodiments, certain applications or partsof the application modules 1222 to 1224 may be executable by otherhardware modules 1280. In certain embodiments, the memory 1220 mayadditionally include secure memory, which may include additionalsecurity controls to prevent copying or other unauthorized access tosecure information.

In some embodiments, the memory 1220 may include an operating system1225 loaded therein. The operating system 1225 may be operable toinitiate the execution of the instructions provided by the applicationmodules 1222 to 1224 and/or manage the other hardware modules 1280, aswell as interfaces with a wireless communication subsystem 1230, whichmay include one or more wireless transceivers. The operating system 1225may be adapted to perform other operations across the components of theelectronic system 1200 including threading, resource management, datastorage control, and other similar functionality.

The wireless communication subsystem 1230 may include, for example, aninfrared communication device, a wireless communication device and/or achipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. The electronic system 1200 may includeone or more antennas 1234 for wireless communication as part of thewireless communication subsystem 1230 or as a separate component coupledto any portion of the electronic system 1200. Depending on the desiredfunctionality, the wireless communication subsystem 1230 may includeseparate transceivers to communicate with base transceiver stations andother wireless devices and access points, which may includecommunicating with different data networks and/or network types, such aswireless wide-area networks (WWANs), wireless local area networks(WLANs), or wireless personal area networks (WPANs). A WWAN may be, forexample, a WiMax (IEEE 802.16) network. A WLAN may be, for example, anIEEE 802.11x network. A WPAN may be, for example, a Bluetooth network,an IEEE 802.15x, or some other types of network. The techniquesdescribed herein may also be used for any combination of WWAN, WLAN,and/or WPAN. The wireless communications subsystem 1230 may permit datato be exchanged with a network, other computer systems, and/or any otherdevices described herein. The wireless communication subsystem 1230 mayinclude a means for transmitting or receiving data, such as identifiersof HMD devices, position data, a geographic map, a heat map, photos, orvideos, using the antenna(s) 1234 and wireless link(s) 1232. Thewireless communication subsystem 1230, the processor(s) 1210, and thememory 1220 may together comprise at least a part of one or more of ameans for performing some functions disclosed herein.

In some embodiments, the electronic system 1200 includes one or moresensors 1290. The sensor(s) 1290 may include, for example, an imagesensor, an accelerometer, a pressure sensor, a temperature sensor, aproximity sensor, a magnetometer, a gyroscope, an inertial sensor (e.g.,a module that combines an accelerometer and a gyroscope), an ambientlight sensor, or any other similar module operable to provide sensoryoutput and/or receive sensory input, such as a depth sensor or aposition sensor. For example, in some implementations, the sensor(s)1290 may include one or more inertial measurement units (IMUs) and/orone or more position sensors. An IMU may generate calibration dataindicating an estimated position of the HMD device relative to aninitial position of the HMD device, based on measurement signalsreceived from one or more of the position sensors. A position sensor maygenerate one or more measurement signals in response to motion of theHMD device. Examples of the position sensors may include, but are notlimited to, one or more accelerometers, one or more gyroscopes, one ormore magnetometers, another suitable type of sensor that detects motion,a type of sensor used for error correction of the IMU, or somecombination thereof. The position sensors may be located external to theIMU, internal to the IMU, or some combination thereof. At least somesensors may use a structured light pattern for sensing.

The electronic system 1200 may further include a display module 1260.The display module 1260 may be a near-eye display, and may graphicallypresent information such as images, videos, and various instructions,from the electronic system 1200 to a user. Such information may bederived from one or more of the application modules 1222 to 1224, avirtual reality engine 1226, the one or more other hardware modules1280, a combination thereof, or any other suitable means for resolvinggraphical content for the user (e.g., by the operating system 1225). Thedisplay module 1260 may include scanning display technology, for exampleusing a two-stage scanning projector as described above.

The electronic system 1200 may further include a user input/outputmodule 1270 allowing a user to send action requests to the electronicsystem 1200. An action request may be a request to perform a particularaction. For example, an action request may be to start or end anapplication or to perform a particular action within the application.The user input/output module 1270 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to theelectronic system 1200. In some embodiments, the user input/outputmodule 1270 may provide haptic feedback to the user in accordance withinstructions received from the electronic system 1200. For example, thehaptic feedback may be provided when an action request is received orhas been performed.

The electronic system 1200 may include a camera 1250 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. The camera 1250 may also be used to take photos or videosof the environment, for example, for VR, AR, or MR applications. Thecamera 1250 may include, for example, a complementarymetal-oxide-semiconductor (CMOS) image sensor, e.g. a silicon sensor,with a few millions or tens of millions of pixels. In someimplementations, the camera 1250 may include two or more cameras thatmay be used to capture 3D images.

In some embodiments, the electronic system 1200 may include a pluralityof other hardware modules 1280. Each of other the hardware modules 1280may be a physical module within the electronic system 1200. While eachof the other hardware modules 1280 may be permanently configured as astructure, some of other hardware modules 1280 may be temporarilyconfigured to perform specific functions or temporarily activated.Examples of the other hardware modules 1280 may include, for example, anaudio output and/or input module (e.g., a microphone or speaker), a nearfield communication (NFC) module, a rechargeable battery, a batterymanagement system, a wired/wireless battery charging system, etc. Insome embodiments, one or more functions of the other hardware modules1280 may be implemented in software.

In some embodiments, the memory 1220 of the electronic system 1200 mayalso store the virtual reality engine 1226. The virtual reality engine1226 may include an executable code of applications within theelectronic system 1200. The virtual reality engine 1226 may receiveposition information, acceleration information, velocity information,predicted future positions, or some combination thereof of the HMDdevice from the various sensors. In some embodiments, the informationreceived by the virtual reality engine 1226 may be used for producing asignal to the display module 1260. For example, if the receivedinformation indicates that the user has looked to the left, the virtualreality engine 1226 may generate content for the wearable display devicethat mirrors the user's movement in a virtual environment. Additionally,the virtual reality engine 1226 may perform an action within anapplication in response to an action request received from userinput/output module 1270 and provide feedback to the user. The providedfeedback may be visual, audible, or haptic feedback. In someimplementations, the processor(s) 1210 may include one or more GPUs thatmay execute the virtual reality engine 1226.

The above-described hardware and modules may be implemented on a singledevice or on multiple devices that can communicate with one anotherusing wired or wireless connections. For example, in someimplementations, some components or modules, such as GPUs, the virtualreality engine 1226, and applications such as, for example, a headsetcalibration application and/or eye-tracking application, may beimplemented on a console separate from the head-mounted display device.In some implementations, one console may be connected to or support morethan one wearable display device.

In some implementations, different and/or additional components may beincluded in the electronic system 1200. Similarly, functionality of oneor more of the components can be distributed among the components in amanner different from the manner described above. For example, in someembodiments, the electronic system 1200 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The hardware used to implement the various illustrative logics, logicalblocks, modules, and circuits described in connection with the aspectsdisclosed herein may be implemented or performed with a general purposeprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but, in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Alternatively, some steps ormethods may be performed by circuitry that is specific to a givenfunction.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments andmodifications, in addition to those described herein, will be apparentto those of ordinary skill in the art from the foregoing description andaccompanying drawings. For example, embodiments may be envisioned inwhich the order of reflection of the input light beam from a scanningreflector and a concave reflector is changed in at least one of thefirst and second scanning stages. Furthermore, in some embodiments oneor both of the scanning reflectors may be configured to have opticalpower, for example the may include a concave mirror, which mayfacilitate the pupil relay. Thus, such other embodiments andmodifications are intended to fall within the scope of the presentdisclosure. Further, although the present disclosure has been describedherein in the context of a particular implementation in a particularenvironment for a particular purpose, those of ordinary skill in the artwill recognize that its usefulness is not limited thereto and that thepresent disclosure may be beneficially implemented in any number ofenvironments for any number of purposes. Accordingly, the claims setforth below should be construed in view of the full breadth and spiritof the present disclosure as described herein.

What is claimed is:
 1. A scanning projector for a display apparatus,comprising: a first scanning reflector configured to steer a light beamin at least a first plane; a second scanning reflector configured tosteer the light beam received from the first scanning reflector in atleast a second plane; and, beam relay optics configured to relay a firstpupil defined at the first scanning reflector to a second pupil definedat the second scanning reflector, and to relay the second pupil to anoutput pupil of the scanning projector, wherein the beam relay opticscomprises a first polarization beam splitter (PBS) and a second PBSdownstream of the first PBS, and wherein at least the second PBS isdisposed in a triple-pass configuration.
 2. The scanning projector ofclaim 1 wherein the second scanning reflector is configured so that thesecond plane is generally orthogonal to the first plane.
 3. The scanningprojector of claim 1 wherein the beam relay optics comprises a firstconcave reflector coupled to the first PBS, wherein the first PBS isdisposed to route the light beam sequentially to the first scanningreflector and to the first concave reflector in a first two passes, andtoward the second scanning reflector in a third pass.
 4. The scanningprojector of claim 3 comprising a waveplate disposed in an optical pathof the light beam for converting a polarization state thereof to anorthogonal polarization state between consecutive passes through thefirst PBS.
 5. The scanning projector of claim 3 comprising a lensdisposed in an optical path of the light beam upstream of the firstscanning reflector.
 6. The scanning projector of claim 5 wherein thelens comprises an output lens disposed at the output pupil.
 7. Thescanning projector of claim 1 wherein the first PBS is disposed todirect the light beam sequentially to the first scanning reflector in afirst pass and to the first concave reflector in a second pass, the beamrelay optics further comprising a second concave reflector coupled tothe second PBS, wherein the second PBS is disposed to direct the lightbeam received from the first PBS sequentially toward the second scanningreflector and toward the second concave reflector in a first two passesthrough the second PBS, and toward the output pupil in a third pass. 8.The scanning projector of claim 7 wherein the beam relay optics furthercomprises four quarter-wave plates (QWP) disposed proximate to the firstscanning reflector, the second scanning reflector, the first concavereflector, and the second concave reflector, for converting apolarization of the light beam to an orthogonal polarization betweenconsecutive passes through each of the first and second PBS.
 9. Thescanning projector of claim 8 wherein the first PBS is disposed todirect the light beam reflected from the first scanning reflector towardthe first concave reflector, and from the first concave reflector towardthe second PBS.
 10. The scanning projector of claim 8 comprising a firstfocusing lens disposed upstream of the first PBS, and an output focusingor collimating lens disposed at the output pupil of the scanningprojector upstream of the second scanning reflector.
 11. The scanningprojector of claim 10 wherein the first focusing lens cooperates withthe first concave reflector to converge the light beam to a focus at anintermediate location in an optical path between the first and secondscanning reflectors.
 12. The scanning projector of claim 10 comprising asecond focusing lens disposed in a double-pass configuration proximateto the second scanning reflector.
 13. The scanning projector of claim 12wherein the first concave reflector and the second focusing lenscooperate to relay the first pupil to the second pupil with amagnification.
 14. The scanning projector of claim 13 wherein the secondscanning reflector is greater in area than the first scanning reflector.15. The scanning projector of claim 2 wherein each of the first andsecond scanning reflectors comprises a tiltable MEMS reflector.
 16. Amethod for forming an image, the method comprising: providing a lightbeam to a first scanning reflector; responsive to a first signal,steering the light beam in at least a first plane with the firstscanning reflector; relaying the light beam from the first scanningreflector onto a second scanning reflector; responsive to a secondsignal, steering the light beam with the second scanning reflector in atleast a second plane; and, relaying the light beam from the secondscanning reflector to an output pupil at an angle defined by steeringangles of the first and second scanning reflectors and substantiallywithout an angle-dependent lateral spatial shift; wherein at least oneof: the relaying the light beam from the first scanning reflector ontothe second scanning reflector, or the relaying the light beam from thesecond scanning reflector to the output pupil, comprises using a firstconcave reflector and a first PBS in a triple-pass configuration. 17.The method of claim 16 comprising using the first PBS and the firstconcave reflector to direct the light beam from the first scanningreflector to the second scanning reflector, and using a second PBS toroute the light beam from the first PBS sequentially toward the secondscanning reflector, and from the second scanning reflector toward theoutput pupil.
 18. The method of claim 17 comprising changing apolarization state of the light beam to an orthogonal polarization statebetween consecutive passes through each of the first and second PBS. 19.A near-eye display (NED) device comprising: a support structure forwearing on a user's head; a light source carried by the supportstructure for providing a light beam; a pupil expander carried by thesupport structure; and, a scanning projector carried by the supportstructure, the scanning projector comprising: a first scanning reflectorconfigured to steer the light beam in at least a first plane; a secondscanning reflector configured to steer the light beam received from thefirst scanning reflector in at least a second plane; and, beam relayoptics configured to relay a first pupil defined at the first scanningreflector to a second pupil defined at the second scanning reflector,and to relay the second pupil to an output pupil of the scanningprojector, the beam relay optics comprising a first polarization beamsplitter (PBS) and a second PBS downstream of the first PBS, and whereinat least the second PBS is disposed in a triple-pass configuration;wherein the pupil expander is configured to expand the output pupil ofthe scanning projector in size for directing the light beam toward aneye of the user.
 20. The NED device of claim 19 wherein the beam relayoptics comprises a concave reflector.